Manufacturers caution against transporting a refrigerator on its back. Moving a refrigerator when it is lying on its back or on its side is likely to cause the appliance's compressor to malfunction.
The compressor in a refrigerator works as a motor, and it uses oil to run the cooling system. If the refrigerator is allowed to lie on its side or on its back, either while it is being moved from one location to another or while it is being stored, the oil is likely to migrate into the lines that are attached to the compressor. The oil does not completely drain from the lines back into the compressor when the refrigerator returns to its standard vertical orientation.